Rotax Starter Issue

Hi all,

I’ve got a Rotax max 125 from about 2016 and never had a single issue with it.
However, I just went to try and start it after about 5 weeks of no running and it was kicking as normal for a bit, nothing out of the ordinary for it considering the fuel had been drained etc. It has the older style starter switch, the red ‘dial’ that you turn to start.
After a couple of kicks, I went to turn it again and nothing happened, no noise at all, no kick, checked spark plug and no spark. I’m assuming there is an issue on the battery side but it’s fully charged and hasn’t been touched at all.

Any suggestions as to what to try is very much appreciated.

How did you determine that the battery was fully charged? Did you use a voltmeter, a load tester or the battery charger saying the battery was charged? If you have a battery store close by, have them test it.

Good point. Just going off the green light on the charger and the fact it has been plugged in for the last 6 weeks. There was also no sign of the battery losing charge, just a sudden loss of everything

I have had this problem with mine (junior pre evo) have you checked if there is nothing isolating the connectors to the battery.

Hope this helps

Thanks for the reply Harry. I don’t think that would be the issue as it was working fine for a few kicks but then nothing, and I didn’t touch anything in between attempts.
Do you remember what it was that was isolating your connectors?

My battery died between sessions, despite my charger saying it was full, and me keeping it charged regularly. They can just change that quickly. The chargers aren’t that great to tell you if the battery has lost capacity. Just if they are charged to their capacity.

Batteries just die. Start with the most obvious, the battery, before doing any unnecessary work. Your charger will charge until the battery will no longer accept a charge. That could be a 12 volts, 9, 6, 3 or 0 volts.
If the battery test good, make yourself a couple of jumper wires with alligator clips at the ends. Three feet of lamp cord should be enough. Mark both ends of one wire so you know which wire is the positive lead. Remove the cable from the starter. Connect the negative jumper to the case of the starter and tap the positive jumper to the input terminal of the starter. If the starter doesn’t spin, fix the starter.
If the starter does spin, you have a harness issue. Unless you have a cable that’s been worn thru, the starter switch would be the next likely candidate. Leave the cable disconnected from the starter. Use a volt meter to read the voltage across the battery terminals. Leave one voltmeter probe connected to the neg battery terminal. Use the other probe to check for voltage at the starter switch. One side of the switch should read close to the reading you got across the battery. The other side of the starter switch should read 0 volts. Keep you volt meter probes where they are and with your third hand, activate the starter switch. That side of the switch should now have voltage.

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Start with the battery and making sure it is good and work your way through the system from there. If you have access to another battery or can borrow one try that first. For that style of rotax switch I have also seen a couple of recurring issues:

  1. The ground under the switch have become loose or buildup has occurred and thus they are not working properly. Solution is to clean and or tighten the contacts
  2. The switch itself has developed play in the plastic. The only solution ive seen for this is temporary. You push down on the switch firmly and then turn. This one is unlikely but ive seen it work before.
  3. The switch has failed completely and requires replacement. The switch eventually seems to wear from vibration which I imagine is the reason for the updated one.

Lastly if none of the above work occasionally the starter will completely die without any prior warning.

The wire for the starter solenoid had come disconnected on my Rotax a few times. It’s a single red wire with s white space connector if I remember correctly. I tightened up the connector a bit and wrapped it in tape.

Liam, Tony, Jack and Brian, thank you very much for taking the time to reply and offer your highly detailed insights. I really appreciate it.
As it turned out the problem was indeed the battery, reading 12V just sitting but only 3.5V when turning the switch to start.
Hopefully the starter switch holds up now.
Once again, many thanks to everyone for taking the time to reply.

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